Method and apparatus for filter selection from a frequency synthesizer data

ABSTRACT

Modern portable communications units, and in particular cellular telephones, can contain several frequency bands for receiving and several frequency bands for transmitting signals. Typically these units contain a baseband unit and a frequency synthesizer unit, which may be embodied as VLSI integrated circuits. The baseband unit commonly contains the user interfaces and control signals for controlling other portions of the circuitry. The second unit is sometimes called a frequency synthesizer unit. The second unit is dedicated to producing frequencies that are used by the communications system to create RF signals for broadcast and also to take RF signals and extract the modulated signal from them for decoding. As personal communications units have begun using an increasing number of bands it is often necessary to configure different filters to receive or broadcast the different bands. Typically, the baseband Integrated Circuit or separate circuitry does this filter configuration management. The data for filter switching, however, can be decoded from the data that is communicated across the serial bus to the frequency synthesizer integrated circuit. By allowing the frequency synthesizer Integrated Circuit to control the filtering as well as the frequency synthesizer functions, integrated circuit pins can be eliminated from the baseband integrated circuit. In addition, timing and latency problems involved with commanding the frequency change over a serial bus and switching filters directly are eliminated.

FIELD OF THE INVENTION

The present invention relates, generally, to systems, processes anddevices which use frequency synthesizers and filters and, in particularembodiments, to processes, systems and devices in which the architectureof frequency synthesizing and filtering stages of communicationtransceivers is improved.

DESCRIPTION OF THE RELATED ART

Portable electronic devices have become part of many aspects ofpersonal, business, and recreational activities and tasks. As thepopularity of various personal communication devices, such as portablephones, portable televisions and personal pagers increases, the demandfor smaller, lighter, more powerful, and more power efficientelectronics, which comprises these devices, has also continued toincrease.

The demand for smaller, lighter, more powerful, and more power efficientelectronics provides motivation for ever increasing levels of circuitintegration, in order to minimize the number of integrated circuits andimprove the functioning of circuits which compose such systems. As thelevels of integration increase and the actual number of integratedcircuits within a system decrease, each integrated circuit may need toperform an increased portion of the functions of the overall system.Accordingly, the integration level of integrated circuits continues toincrease as the number of integrated circuits within such systemscontinues to shrink. As more functions are integrated into fewer andfewer integrated circuit packages the number of pins on integratedcircuits, i.e. input and output connections, has risen. As the levels ofintegration, of integrated circuits, increase, circuit packaging andinput output pin count become critical design considerations.

Integrated circuits for communication systems must also be concernedwith interoperability, that is integrated circuits from one manufacturermust be able to work with a variety of other manufacturers' integratedcircuits. The more integrated circuits that a manufacturer's product iscompatible with the more integrated circuits that that manufacturer maysell. Because of the desire for interoperability, various manufacturersoften develop similar interfaces between different integrated circuits.The need for common interfaces is increasingly important as higherdensity integrated circuits integrate more functions. As more functionsare integrated, there is a need for more input output connections toconnect the ever-increasing number of functions, within an integratedcircuit, to the outside world. To meet the increasing input/output needsof increasingly complex integrated circuits, manufacturers have turnedto multiplexed input and output pins, serial and parallel busses toconvey information between parts.

Some of the buses, such as the serial I²C bus, are standardized and welldefined. Others may adopt similar physical connections, so that theinterconnections between parts become de facto standards and only thedata communicated is changed, depending on which manufacturer's devicesare being used. One such de facto standard is the serial bus used by thebaseband electronics in communications circuits to communicate with thesynthesizer portion of the circuitry. The baseband portion of thecommunications system circuitry is a portion of the circuitry that isused for controlling the system. It commonly includes logic circuitry tocontrol other subsystems, and may control the receiving and processingof commands from the user of the system as well as displays. Thesynthesizer portion of the circuitry is the portion that commonlycontrols the synthesis of frequencies for modulating and demodulatingsignals. Examples of frequency synthesizers controlled by serial bussesare the MB15E07SL integrated circuit produced by Fujitsu, the LMX2326produced by National Semiconductor, and the MC145202 produced byMotorola.

Commonly included with a baseband electronics section and a synthesizerelectronics section is a filtering section. A filtering section istypically separate from a synthesizer portion of the circuitry andcontains discrete filtering elements. If only one transmit band and onereceive frequency band is used, within a communications unit, theassociated bandpass filters used with those frequency bands may behardwired into the circuit, as they would never need to be changed. Moreand more modern communications devices, however, are required to operatein several communications bands and have the ability to be switchedbetween the bands. An example of a communication system being requiredto support more than one band is the Japanese Personal Digital CellularSystem (PDC). An additional allocation of bandwidth for the JapanesePersonal Digital Cellular (PDC) system has required handset radios tosupport communication channels in three separate receive and transmitfrequency bands. Existing SAW (Surface Acoustic Wave) filters, such asthe PDC800 produced by Fujitsu, which are commonly used in suchapplications, can be only used to support one or two of the bands at atime. Because the SAW filters can be used to support only one or two ofthe bands at a time methods for selecting correct filters for a givencommunication channel need to be devised.

It is common practice to have an embedded processor control suchsubsystems. The straightforward approach to solving the filter/bandselection problem is to add, to the embedded processor subsystem,digital logic and control signals to switch bandpass filters. Thecontrol signals needed may be supplied to circuitry external to theembedded processor subsystem. Embodiments of the present disclosuredispense with the straightforward solution of adding digital logic andcontrol signals to the embedded processor subsystem.

SUMMARY OF THE DISCLOSURE

Accordingly, preferred embodiments of the present invention are directedto frequency synthesis and filter selection circuitry, and systemsemploying the same. Embodiments described herein relate to methods andapparatus for improving control over the selection of bandpass filters,in systems where more than one filter is present. External circuitry canthen direct signals through the appropriate filters. Embodiments of thepresent invention instead use the data which is used to program thefrequency synthesizer circuits to control filter selection. By decodingthe data from the signals used to program the frequency synthesizer,logic circuitry can determine which frequency is being synthesized, andhence which filter is required. By decoding the data used to program thefrequency synthesizer and using it to control the selection of filtersthe need for additional logic and control signals to select filters canthereby be eliminated.

The elimination of additional control signals to select filters, resultsin a reduction of the number of connections between the filter selectioncircuits and the embedded processor subsystem. This reduction savesspace, makes for easier circuit board layout, and reduces test time ofthe baseband processor Integrated Circuit by reducing the amount of I/Opins which must be tested. In addition, designs are simpler becausesoftware, logic circuits and other circuitry, which might have beenrequired to drive the additional control circuits, are no longer needed.

An illustrative embodiment of the present invention includes apparatusfor producing and detecting radio frequencies. This illustrativeembodiment includes a first unit that generates serial bus data, and aserial bus, coupled to the first unit that receives the serial bus datathat is provided to it. This illustrative embodiment also includes asecond unit, coupled to the serial bus, for accepting the serial busdata and creating second unit control signals, from the serial bus data.A frequency signal generating mechanism is included within the secondunit. The second unit has inputs for accepting control signals andgenerating a frequency signal based on those control signals. The secondunit also activates one of the filters and deactivates the remainingfilters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram representing a system environment according toan example embodiment of the present invention.

FIG. 2 is a more detailed block diagram representation of transmit andreceive functions as may be found in the exemplary portablecommunication system in FIG. 1.

FIG. 3 is block diagrams representing a system interconnect arrangement,such as may be found in a portable telephone containing two transmit andtwo receive filters.

FIG. 4 is an enhanced detail block diagram of a Base Band Electronicsunit, such as the unit shown in block 317 of FIG. 3.

FIG. 5 is a functional block diagram of a frequency synthesizer, such asthe frequency synthesizer shown in block 313 of FIG. 3.

FIG. 6a is a block diagram of a preferred embodiment of the invention.

FIG. 6b is block diagram of an exemplary filter selection mechanism,according to an embodiment of the invention.

FIG. 7 is a chart showing the relationship of the data lines logicvalues to the frequency of the synthesizer and to the filter used.

FIG. 8 is a block diagram of a preferred embodiment of the invention.

FIG. 9 is a chart showing the relationship of data line value to thesynthesizer frequency and bandpass filter selected, for example, in theembodiment depicted in FIG. 8.

FIG. 10 is a block diagram of an embodiment of the inventionincorporating the filter selection circuits and mixers into thefrequency synthesizer unit.

FIG. 11 is a flowchart showing a method for controlling filterselection, according to an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description of preferred embodiments, reference is madeto the accompanying drawings, which form a part thereof, and in which isshown, by way of illustration, specific embodiments in which theinvention may be practiced. It should be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present disclosure.

In addition, the present disclosure is illustrated by use of examplesreferenced to portable communication unit such as a portable phone. Itis to be understood that, although the present invention is useful inthe portable telephone art, the present invention is applicable to avariety of systems that employ frequency synthesis and filteringmechanisms. Illustrative embodiments presented are by way of example andare not to be construed as limiting the usefulness or applicability ofthe present invention.

To realize a cost-efficient design, portable telephone manufacturers mayattempt to minimize size, weight, complexity, and power consumption.Embodiments of the present invention therefore relate to portablecommunication transceivers in which bandpass filters may be switchedusing frequency synthesizer data. It should be noted, however, thatfrequency synthesizers and filtering stages that accompany them,according to embodiments of the present invention, are not unique toportable communications. Frequency synthesizers and filtering stages maybe employed in a variety of electronics, including both wirelesstransmission systems as well as wired systems. For purposes ofsimplifying the present disclosure, however, preferred embodiments ofthe present invention are described in relation to personal wirelesscommunications systems, including, but not limited to digital mobiletelephones, digital cordless telephones and the like. Such personalcommunications systems typically include one or more portablereceiver/transmitter units.

A generalized representation of a system environment, according to anembodiment of the present invention, is shown in FIG. 1. In FIG. 1 aportable communications system 101 communicates with a base stationreceiving and broadcast unit 103. The portable communications system101, communicates with the base station 103, receiving informationacross a communications channel 109 and sending information across asecond communications channel 107. The receive and send channels, 107and 109, may be the same channel, different channels or even channelswhich change with time. The base station 103 couples the communicationsof the portable communications system 101 into a node 105, which is anaccess point into the land based phone system. Portable communicationssystem 101, includes both transmit and receive sections as generallyillustrated in FIG. 2.

FIG. 2 represents, in detail, transmit and the receive functions as maybe found in a portable communication system, such as, for example, theportable communications system 101. In the present illustrativeembodiment, the signal source may include, for example, a microphone 201for converting sound waves into electronic signals representative of thesound waves. The electronic signals representative of the sound wavesare then coupled to a transmitter 203. The transmitter unit 203receives, from the microphone 201, the electronic signals, whichrepresents the sound waves, and modulates a carrier signal with arepresentation of them. The transmitter, 203, amplifies the modulatedsignal and otherwise prepares the electronic signals, for transmission.The signals, which have been prepared for transmission, are provided toa duplexer 205, which then further couples the signals into an antenna211, for the purpose of broadcasting the signal via radio transmission.In other embodiments, the signal source may include any suitable devicefor producing data signals for communication over channel 107 such as,but not limited to, a keyboard, a digital voice encoder, a mouse orother user input device, a sensor, monitor, testing apparatus, or thelike.

A portable communication system 101 may also include a receiving antenna211 for the reception of signals. In the portion of the example portablecommunication system shown in FIG. 2 the antenna 211 is coupled to aduplexer 205, which then provides the received signals to the receiverunit 207. The receiver unit 207 demodulates, amplifies and otherwiseprocesses the received signal and provides it to a speaker 209. Thespeaker transforms provided signal into sound waves, which may then beperceived by a user. In other embodiments the signal received mayrepresent other information other than voice, such as, but not limitedto data input to a computer, remote telemetry, fax data, or the like.

FIG. 3 is a detailed block diagram of the illustrative portablecommunications system, of FIG. 2. For illustration purposes, it may beassumed that the portable communications system, is a Japanese PersonalDigital Cellular (PDC) telephone. This example is chosen because it willbe particularly illustrative, as a real world example, when describingthe disclosure herein. Those skilled in the art will recognize that thedisclosure, while useful in this application, is not limited to thisapplication, and that the disclosure may be applied in a variety ofdifferent systems in a variety of different ways. A microphone 301, isused to accept the user's voice and convert it into an electricalsignal, representative of the user's voice. The electrical signalrepresenting the user's voice is then provided to the input circuitry303, where it is amplified and digitized. The digitized voice signal isthen provided to a modulator 305 where it is used to modulate a carriersignal. The modulated signal is then provided to a mixer 307, where itis mixed with a signal provided to the mixer 307 by a frequencysynthesizer unit 313. The mixer 307 translates the frequency of themodulated signal to the proper frequency for broadcast. The broadcastsignal is then provided to either filter 309 or filter 311 as controlledby the baseband electronics 317. The baseband electronics uses solidstate switch 337, or solid state switch 339 to select which filter thebroadcast signal will be coupled to. The selected filter then attenuatesany undesired frequency components, and passes the desired components.The filtered transmission signal is then coupled into the amplifier andduplexer block 319, where it is amplified, by the amplifier, andcoupled, via the duplexer, into antenna 321, for broadcast via radiotransmission.

In the present embodiment two filters, a first filter 309 and a secondfilter 311, are present. These filters commonly may be SAW (SurfaceAcoustic Wave) filters, which are very effective in this type ofapplication. Current SAW filters do have a limitation, however, thatthey can filter only frequency bands that are about 5% of their nominalcenter frequencies. For this reason there are two filters, i.e. to coverthe necessary frequency bands. Japanese Personal Digital Cellular (PDC)telephones, as illustrated in the present embodiment, utilize threeseparate frequency bands to transmit and to receive signals. Because oneSAW filter can only cover two of the bands, a second filter is needed.The filters are then commonly switched as the broadcast frequency ischanged. A straightforward approach to the switching of filters is toallow a baseband electronics unit, such as 317, to control the switchingof the filters as just described. The baseband electronics unit maytypically be the overall controller for the telephone. The basebandelectronics unit may commonly accept input commands from the user andthen control the other subsystems within the telephone.

The serial bus 315 interconnection, for controlling the frequencysynthesizer, has become somewhat of a de-facto standard in the industry,typically containing data, clock, and latch enable lines. The serial bus315, couples programming data to the frequency synthesizer 313, so thatthe frequency synthesizer, 313 synthesizes and delivers the correctfrequency to the mixer 307, thereby assuring that the proper frequencyband for broadcast is chosen.

The signal received by the antenna 321 is coupled into the duplexer andAmplifier block 319. The received and amplified signal is then coupledinto either filter 329, or filter 331, depending on which frequency bandis being received. The frequency band being received, and hence theselection of filter 329 or filter 331, is commonly controlled by abaseband electronics unit in a manner similar to the selection of theselection of filter 309 or filter 311, in the broadcast portion of thesystem. The baseband electronics uses solid state switch 333, or solidstate switch 335 to select which filter the received signal will becoupled to. The serial bus can be used to control the frequencysynthesizer 313 for the receive side of the phone. The frequencysynthesizer 313, provides the correct frequency to the receive mixer327, to translate the received signal to the correct frequency for thedemodulator 325. The demodulator 325 demodulates the signal received andcouples it to the output circuitry 323. The output circuitry thenprocesses the demodulated signal suitably for presentation to thespeaker 321, where the original voice signal is reproduced forperception by the user.

It will be apparent to those skilled in the art that the foregoingdescription is one of example only. There are many modifications andvariations of ways to interconnect the circuitry to implement theelectronic functions illustratively described, and still preserve theessential functioning of the personal communications unit.

FIG. 4 is a block diagram illustrating, with increased detail, thefunctioning of the baseband electronics unit 317. FIG. 4 illustrates anapproach to controlling the frequency synthesizer and selecting bandpassfilters. In FIG. 4 a baseband electronics unit 401, may be typicallycontained within one integrated circuit package. A baseband processor421, is the controller for the baseband electronics unit 401. Thebaseband processor 421, receives user input 423 in the form of keystrokecommands. The baseband processor 421, may also prompt the user withaudio and visual cues (not shown). The baseband processor 421, processesthe user input 423, and controls the baseband unit 401, to select thecorrect sending and receiving bands, initiate a call, and control theother functions within the phone.

The baseband processor 421, provides a signal to a receive filtercontrol unit 407, for selecting the appropriate filter to match thebroadcast band that has been chosen. The receive filter control unit 407accepts the signal from the baseband processor 421 and stores the filterselection in a register that provides a filter select signal 403. Thefilter select signal 403 signal controls filter select circuitry 405,which activates the appropriate filter. Filter circuitry may be embodiedin solid state switch circuits, for example, 333 and 335.

The baseband processor 421, also provides a signal to the transmitfilter control unit 425, for selecting the appropriate filter to matchthe transmit band that has been chosen. The transmit filter control unit425 accepts the signal from the baseband processor 421 and then storesthe filter selection in an output register that provides a filter selectsignal 427. The filter select signal 427 controls filter selectcircuitry 429 that then activates the appropriate filter. Filtercircuitry may be embodied in solid state switch circuits, for example,337 and 339.

The baseband processor 421, also interfaces with the serial dataregister 419. The serial data register 419 receives the data, necessaryto program the frequency synthesizer unit 313, from the basebandprocessor 421. This data may vary depending on the manufacturer of thefrequency synthesizer unit 313, because, although the serial busconnections may be standardized between manufacturers, the data used toprogram the units can be different. The data necessary to program thefrequency synthesizer unit is then coupled through the serial data line409, to the frequency synthesizer unit 313. The serial data transferfrom the baseband electronics unit 401, to the frequency synthesizer501, is synchronized by the clock 411, which is provided by the basebandprocessor 421. The baseband processor also provides the data latchsignal 413. The data latch signal 413, is coupled to the frequencysynthesizer unit 501, and signals the frequency synthesizer unit 501,when the serial data 409, is valid.

FIG. 5 is a block diagram illustrating the functioning of a frequencysynthesizer unit 501. A serial bus 517, is coupled to a serial bus datadecoder 515. The serial bus data decoder 515, accepts and decodes theserial data provided to it by a baseband electronics unit 401, by meansof the serial bus 517.

The serial bus data decoder 515, decodes information indicating whichfrequency must be provided to the transmit mixer, 503. The decodedserial bus information is coupled to the transmit frequency sourceselect block 505, using the Transmit frequency select lines 513. Thetransmit frequency source select block 505 then selects the properfrequency, as indicated by the data from the serial bus data decoder515, from one of the three transmit frequency sources, 507, 509 and 511.The selected transmit frequency source is then coupled into the transmitmixer 503, where it is used to mix with the modulated signal and providethe correct frequency for broadcast.

The serial bus data decoder 515, also decodes information indicatingwhich frequency must be provided to the receive mixer 529. The decodedserial bus information is coupled to the receive frequency source selectblock 527, using the receive frequency select lines 525. The receivefrequency source select block 527 then selects the proper frequency, asindicated by the data from the serial bus data decoder 515, from one ofthe three receive frequency sources 519, 521 and 523. The selectedreceive frequency source is then coupled into the receive mixer 529where it is used to mix with the modulated signal and provide thecorrect frequency for broadcast.

Thus the baseband electronics unit 401 selects the frequencies that theportable communications system, illustratively the PDC phone, will useto broadcast and receive. The baseband electronics unit 401, may thenselect the proper filters to be used with the transmit and receivefrequencies chosen. The broadcast and receive bandpass filter selectsignals 403 and 427 are used to control the receive and broadcast filterselection, as appropriate. The baseband electronics unit 401 alsocouples the information concerning which frequencies will be used totransmit and receive to the serial bus 417, for further coupling to thefrequency synthesizer unit 501. The frequency synthesizer unit 501,accepts the data from the serial bus 517, and decodes it to ascertainwhich frequency source will be provided to the receive mixer 529 andwhich will be provided to the transmit mixer 503.

It will be recognized by those skilled in the arts that the foregoingdescription is used for illustrative purposes only and that variousimplementations can vary considerably from the one described. Forexample, the frequency of the signal provided to the transmit mixer isshown as being selected from three discrete frequency sources by afrequency source select block 505. In an actual implementation, theremay not be three discrete frequency sources present. Because of costconsiderations it is likely the three different frequencies will begenerated by a single source, this is multiplied or divided asappropriate. Dividers may generate the frequencies, as may phase lockloops, multipliers, crystals, or other devices using schemes well knownin the art. The three transmit frequency sources 507, 509, and 511 andthe three receive frequency sources 519, 521, and 523, are usedillustratively, in order to provide an understanding of the functioningof the circuit.

FIG. 6a is an exemplary functional block diagram, of a preferredembodiment, of the invention. In FIG. 6a, the baseband unit 621 iscoupled via a serial bus 619 to the bus data decoder 617 The bus datadecoder 617, is coupled to the transmit frequency source select 609 viadata lines 605, 607 and 649. The data lines 605, 607 and 649, controlthe selection of frequency, which is provided to the transmit mixer 603,according to the Frequency-Filter Select Table shown in FIG. 7. If thetransmit frequency source to be selected is 611, filter 641 will beactivated and data values lines 605, 607, and 649 will have data values“1”, “0”, “0” coupled to their respective lines from the bus datadecoder 617. If the transmit frequency to be selected is 613, filter 641will again be activated and data lines 605, 607, and 649 will again havedata values “1”, “0”, “1” coupled to the respective lines from the busdata decoder 617. If the transmit frequency to be selected is 615,filter 643 will be activated and data lines 605, 607, and 649 will havedata “0”, “1”, “X” (“X”=don't care state, i.e. either a “1” or a “0”)coupled to their respective lines from the bus data decoder, 617.Typically filters may not have activate inputs to turn them on and off.If they do not an alternative common approach is illustrated in FIG. 6b.FIG. 6b is block diagram of an exemplary filter selection mechanism,according to an aspect of the invention. In order to select filter 651,a control signal is applied to solid state switches 655 and 653 usingfilter control 661. When solid state switches 655 and 653 are activatedthe filter 651 is coupled to the input 657 and output 659 of the filterselection module and the filter 651 is activated. When solid stateswitches 655 and 653 are deactivated the filter 651 is decoupled fromthe input 657 and output 659 of the filter selection module and thefilter 651 is deactivated.

Similarly the bus data decoder 617 is coupled to the receive frequencysource select 631 via data lines 637, 635 and 651. These three datalines 637, 635 and 651, control the selection of frequency, which isprovided to the receive mixer 633, according to the Frequency-FilterSelect Table shown in FIG. 7. If the receive frequency to be selected is625, filter 647 will be activated and data lines 637, 635 and 651 willhave data logic levels “1”, “0”, “0” coupled to their respective linesfrom the bus data decoder, 617. If the receive frequency to be selectedis 627, filter 647, will again be activated and data lines 637, 635 and651 will have data logic levels “1”, “0”, “1” coupled to theirrespective lines from the bus data decoder, 617. If the transmitfrequency to be selected is 629, filter 645 will be activated and datalines 637, 635 and 651 will have data logic levels “0”, “1”, “X”(“X”=don't care state, i.e. either a 1 or a 0) coupled to theirrespective lines, from the bus data decoder 617.

The receive and transmit signals, so selected, are coupled to theduplexer and amplifier 623, and thereby to the antenna 639 in the samemanner as the FIG. 3, current art embodiment.

In the current embodiment of the disclosure, as shown in FIG. 6a, thebaseband unit 621, does not contain the filter select signals as theapproach illustrated in FIG. 3, does. Instead of controlling the filterselect from the baseband unit 621, that function is relegated to thefrequency synthesizer unit 601. This arrangement provides severaladvantages to the designer who is attempting to design and integrate abaseband unit with a frequency synthesizer unit into a complete system.The first of the advantages is that it saves four integrated circuitpins in a baseband integrated circuit, as compared to a conventionalbaseband design. The pins saved are dedicated pins, that must bemaintained at a logic level at all times to properly select the filterswhich will be used. If the pins are not dedicated pins, i.e. are pins onwhich the data is valid for only certain time periods, then another datavalid pin would need to be added to ensure that only valid data on thelines are used to select the filters to be used.

The reduction in Baseband unit pins provides several advantages. Itenables the baseband unit pins, which are saved, to be used for otherpurposes, thereby increasing the functionality that can be containedwithin the baseband integrated circuit and communicated to the outsideworld. Another advantage is that it eliminates the testing of those pinsso it can shorten the time for the testing of the baseband integratedcircuit. A further advantage is that the filter control signals from thebaseband integrated circuit are no longer needed, and the circuitry andcircuit board layout may be simplified. In addition there is theadvantage that the filter control signals and the frequency synthesisfunction are now within one integrated circuit (the frequencysynthesizer) instead of being contained partly in the basebandintegrated circuit and partially within the frequency synthesizercircuit. Combining both related control functions within the samecircuit eliminates the timing problems, which can occur if the selectionof the frequency to the mixer and the filter selection are notaccomplished simultaneously. Commonly the filters are selected directlyfrom circuitry within the baseband electronics portion of the circuit,or from added control circuitry. The frequencies coupled to the mixercircuits would, however, be selected as a consequence of informationdelivered via the serial bus. Receiving and decoding serial businformation and then coupling the correct frequency into the mixerstakes time. If the selection of the filters and the coupling of theproper frequency into the mixer are not simultaneous, interference ornoise may result, degrading the perceived quality of the unit. Theselection of the filters and the coupling of the proper frequency intothe mixer can be timed to coincide. Frequency synthesizer integratedcircuits from different manufacturers, however, may perform thefrequency synthesis function differently, producing different latenciesbetween the coupling of the data to the serial bus and in the productionof the frequencies to be coupled into the mixers. By consolidating thefunctions of selecting the filters and the coupling of the properfrequency into the mixer within one integrated circuit, the selection ofthe filters and the coupling of the proper frequency into the mixer canbe easily synchronized, thus eliminating timing problems. Placing thecontrol of the selection of the filters and the coupling of the properfrequency into the mixer within the frequency synthesizer integratedcircuit, also creates the possibility of bringing the mixer andfiltering functions into the frequency synthesizer integrated circuit.

FIG. 8 is a block diagram of a second preferred embodiment of thedisclosure. The second preferred embodiment of the disclosure is similarto the first preferred embodiment, illustrated in FIG. 6a. In both thefirst and second embodiments, the filter select function has been movedout of the baseband Unit 621 and into the frequency synthesizer unit601. Filter 641, of FIG. 6a has been replaced by filter 801, of FIG. 8.Filter 801, is of a type that is activated by a logic “0” instead of alogic “1”. filter 801, of FIG. 8 is activated by a logic “0” on dataline 605, and Filter 643, of FIG. 8 is activated by a logic “1” on dataline 605. In other words when filter 801, is activated Filter 643, isdeactivated. Similarly, filter 647, of FIG. 6a has been replaced byFilter 803, of FIG. 8. Filter 803, of FIG. 8 is similar to filter 801,in that filter 803, is of a type that is activated by a logic “0”instead of a logic “1”. Filter 803, of FIG. 8 is activated by a logic“0” on data line 637, and filter 645, of FIG. 8 is activated by a logic“1” on data line 635. In other words when filter 645, is activatedfilter 803 is deactivated. This situation is summarized in the table ofFIG. 9. If the transmit frequency source of 611 or 613 is to beactivated then data line 607 will have a logic “0” value coupled to itwhich will activate filter 801, and deactivate filter 643. If thetransmit frequency source of 615 is to be activated, then data line 607will be a logic “1” that will deactivate filter 801, and activate filter643. Similarly if the transmit frequency source of 625 or 627 is to beactivated then data line 635 will have a logic “0” coupled to it whichwill activate filter 803, and deactivate filter 645. If the transmitfrequency source of 629 is to be activated then data line 635 will havea logic “1” coupled to it which will deactivate filter 803 and activatefilter 645. By choosing filters with complimentary activation inputs andcorrectly coding the bus data decoder data lines, the bandpass filtersfor transmit and receive can be selected with a single external pin forthe transmit stage and a single external pin for the receive stage.

In a third preferred embodiment in FIG. 10 the mixers and the filterselection circuits are combined into one integrated circuit 1001. Theintegrated circuit components are identified as being within the dottedline of the illustration in FIG. 10. This embodiment conserves IC pinsover a prior art embodiment in which the filter selection is controlledby separate circuitry. In other words, by selecting the transmit andreceive filters by using the frequency synthesizer data, control linesto the filters from the baseband unit 621 can be avoided. This can allowthe transmit mixer 603, receive mixer 633, as well as filter selectioncircuits 1003 and 1009 to be integrated into one package as shown by1015.

A method for controlling filter selection is illustrated in theflowchart shown in FIG. 11. In one embodiment of the method shown inFIG. 11, controlling filter selection comprises producing control datain a first unit, as shown at 1102. The control data is then transmittedfrom the first unit to a second unit, as shown at 1104. The control datais then accepted by the second unit, as shown at 1106. In oneembodiment, the first unit may be a baseband unit of a portablecommunication unit, and the second unit may comprise a frequencysynthesizer. In one embodiment, the first unit may be coupled to aserial bus that receives control data as serial bus data that isprovided to it. The second unit may also be coupled to the serial bus,for accepting the control data as serial bus data.

A frequency signal is then generated within the second unit usingcontrol data, as shown at 1108. In one embodiment, the frequency isgenerated by a frequency synthesizer within the second unit. In oneembodiment, the control data is also used to enable at least one filterfrom a plurality of filters and disable the remaining filters using thecontrol data, as shown at 1110.

Those skilled in the art will recognize that the techniques of thisdisclosure may be extended and modified to meet the needs of particularimplementations, without departing from the spirit and the substance ofthe disclosure. Those skilled in the art will also recognize that theillustrative implementations in the disclosure serve as explanationonly, and not as limits to the invention, which is defined by the claimsappended below.

We claim:
 1. An apparatus for controlling a filter selection circuit,the apparatus comprising: a first unit for generating control data; adata bus coupled to the first unit for receiving the control data; asecond unit, coupled to the data bus, for accepting the control data andcreating second unit control signals from the control data; a frequencygenerating mechanism within the second unit, for accepting second unitcontrol signals and generating a frequency signal based on the secondunit control signals; and a filter selection circuit for selectivelyactivating at least one of a plurality of filters for filtering saidfrequency signal based on the second unit control signals.
 2. Anapparatus as in claim 1 wherein the data bus further comprises a serialbus.
 3. An apparatus as in claim 1 wherein the first unit furthercomprises: an input for accepting frequency generating commands; and acircuit for converting the frequency generating commands into controldata.
 4. An apparatus as in claim 1, wherein the first unit is containedwithin an integrated circuit.
 5. An apparatus as in claim 1, wherein thesecond unit is contained within an integrated circuit.
 6. An apparatusas in claim 1 wherein: the first unit is contained within a firstintegrated circuit; the second unit is contained within a secondintegrated circuit; and the data bus connects the first unit to thesecond unit.
 7. An apparatus as in claim 6 wherein the data bus is aserial bus.
 8. An apparatus as in claim 1 wherein the first unit is abaseband unit of a communications unit.
 9. An apparatus as in claim 1wherein the second unit is a frequency synthesizer unit of acommunications unit.
 10. An apparatus as in claim 5 wherein the data busis a serial bus.
 11. A method for controlling filter selection, themethod comprising: producing control data for controlling a frequency;using the control data to cause a frequency signal to be generated by afrequency synthesizer; and utilizing the control data to enable at leastone filter from a plurality of filters; and filtering the frequencysignal with at least one of said enabled filters, wherein the step ofproducing control data for controlling a frequency comprises producing,within a first unit, control data for controlling a frequency in asecond unit, further comprising transmitting the control data from afirst unit and accepting the control data within a second unit, whereinthe step of transmitting the control data from a first unit furthercomprises coupling the control data to a data bus, and the step ofaccepting the control data within a second unit further comprisesaccepting the control data from the data bus in a second unit, whereinthe step of coupling the control data to a data bus comprises couplingserial control data to a serial data bus.
 12. A method for controllingfilter selection, the method comprising: producing control data forcontrolling a frequency; using the control data to cause a frequencysignal to be generated by a frequency synthesizer; and utilizing thecontrol data to enable at least one filter from a plurality of filters;and filtering the frequency signal with at least one of said enabledfilters, wherein the step of producing control data for controlling afrequency comprises producing, within a first unit, control data forcontrolling a frequency in a second unit, further comprisingtransmitting the control data from a first unit and accepting thecontrol data within a second unit, wherein the step of transmitting thecontrol data from a first unit further comprises coupling the controldata to a data bus, and the step of accepting the control data within asecond unit further comprises accepting the control data from the databus in a second unit, wherein the step of producing, within a firstunit, control data for controlling a frequency in a second unitcomprises producing control data within a baseband unit of a portablecommunication unit for controlling a frequency in a frequencysynthesizer in the portable communication unit.
 13. A method forcontrolling filter selection, the method comprising: producing controldata for controlling a frequency within a first unit; coupling thecontrol data to a data bus; accepting the control data from the data busin a second unit; using the control data to cause a frequency signal tobe generated by a frequency synthesizer; and using the control data todisable at least one filter from a plurality of filters, wherein thestep of coupling the control data to a data bus comprises couplingserial control data to a serial data bus.
 14. A method for controllingfilter selection, the method comprising: producing control data forcontrolling a frequency within a first unit; coupling the control datato a data bus; accepting the control data from the data bus in a secondunit; using the control data to cause a frequency signal to be generatedby a frequency synthesizer; and using the control data to disable atleast one filter from a plurality of filters, wherein the step ofaccepting the control data from the data bus comprises accepting serialcontrol data from a serial data bus.
 15. A method for controlling filterselection, the method comprising: producing control data for controllinga frequency within a first unit; coupling the control data to a databus; accepting the control data from the data bus in a second unit;using the control data to cause a frequency signal to be generated by afrequency synthesizer; and using the control data to disable at leastone filter from a plurality of filters, wherein the step of producing,within a first unit, control data for controlling a frequency in asecond unit comprises producing control data within a baseband unit of aportable communication unit for controlling a frequency in a frequencysynthesizer in the portable communication unit.